Optical Properties of Atmospheric Aerosols and Their Application in the Radiative Transfer Model
|School||Chinese Academy of Meteorological Sciences|
|Course||Atmospheric Physics and Atmospheric Environment|
|Keywords||atmospheric aerosols optical properties non-spherical dust-like aerosols nitrate aerosols radiative transfer model|
Atmospheric aerosol plays an important role in global and regional climate change, and its impact on climate change and environment problem has caused worldwide concern. How accurately and efficiently to calculate the optical properties of atmospheric aerosols and how to describe and set the impact of optical properties on the radiative transfer have become a hot and difficult problem in the research of radiative forcing of climate change. The paper involves four parts are as follows:1. The optical properties of nonspherical dust-like aerosols from 0.2-40μm wavelength were calculated by a combination of T-matrix method and an improved geometric optics method in this work under the condition of a representative shape distribution and size distribution. By comparing the optical properties of dust particles between nonspherical and equivalent volume sphere hypothesis, we found that, (1) the shape of dust-like aerosols has a smaller influence on the extinction efficiency factor, scattering albedo and asymmetry factor compared to the size distribution; (2) The difference of phase function between nonspherical and spherical dust-like aerosols in the shortwave region is significant, especially in the visible region, and it changes with different scattering angles, the phase functions of nonspheical paticles demonstrate nearly perfect resemblance to the phase functions measured for dust-like aerosols; (3) In shortwave region, the extinction-to-backscatter ratio in the so-called lidar equation is affected by the shape of dust-like aerosols greatly, therefore, the nonspherical effects should be considered in the retrieval of dust optical depth by using the lidar equation.2. By comparing the optical properties of nitrate and sulfate aerosols, we find that the main differences between the two kinds of aerosols are the extinction efficiency factor and single scattering albedo. The difference of extinction efficiency factor not only has close relationship with the wavelength, but also changes with the relative humidity greatly. The difference of single scattering albedo shows an obvious change at special wavelength and relative humidity. For example, when the wavelength is nearly 2.8μm and the relative humidity is below 40%, theωfor nitrates are about 40% greater than those for sulfates.3. To calculate the reflectivity of spheroid and sphere dust-like, the optical properties of spheroid and sphere dust-like aerosols has been put into the Disortδ-256 radiative transfer model, and the corresponding analysis has been done in the paper. We found that, the impact of the shape of dust-like aerosols on the relectivity in the shortwave is more obvious than it in the longwave region, the difference of relectivity between spheroid and sphere dust-like in the visible band is specifically obvious, and the difference in the visible band becomes lager with the decrease of the optical depth.4. Due to the inherent shortcoming of the parameter table in the RAD_BCC radiative transfer model, we have updated the parameter table, and made a new parameter including six kinds of optical properties of six kinds of aerosols at 17 spectral bands, 12 size distributions and 10 relative humidity, and the non-spherical effect has been considere for dust-like aerosols in the new parameter table. According to the result style of the RAD_BCC radiative transfer model, the process of making the new parameter table has been worked out in this paper, and the validity of the new parameter table has been checked by comparing results of the new and old parameter table. The new parameter table can provide efficiency input of aerosol parameters for the RAD_BCC radiative transfer model.